Electric heat regulating switch



July 2, 1957 R. COLLIER I 2,798,131

ELECTRIC HEAT REGULATING swncu Filed May 14, 1954 2 Sheets-Sheet 2 'a'a/mep Caz ER United States Patent M 2,798,131 ELECTRIC HEAT REGULATING'SWITCH Richard Collier, Esher, England Application May 14, 1954, Serial No. 429,933

Claims priority, application Great Britain October 19, 1953 Claims. (Cl.200=-122) This invention relates to an electric heat regulating switch of the type adapted to operate cyclically under the control of a thermal element which regulates the overall heating eifect of the current supply by controlling the relative durations of the periods in each cycle during which the switch is closed and open respectively. This type of switch is particularly useful for controlling the hotplates of electric cookers'and enables the heating effect of such hotplates to be regulated so that they can beused efficiently for simmering.

The present invention provides an'improved switch'of this type which is simple, reliable,'inexp.ensive to manufacture andeasily adjustable overa'wide range, so that the periodduring whichthe current is'switched on in each cycle can be varied from almost the whole duration of the cycle to only a small fraction thereof.

More specifically 'the object of this invention is the provision of a switch of the type referred to comprising a pivotal bimetallic strip and switch'plate in which the pivotal connection is of simpler construction than hitherto and'in 'which the strip and-plate are'readily assembled.

Another object of the invention is to enable'said-strip and plate to be removed'and replaced in a simple manner.

Yet a further object is to provide a spring connection between'the bimetallic strip and the switch plate whereby theplate has a snap over action and to utilise said spring to maintain pivotal connection between said strip and plate and hearing or supportmembers therefor.

Anotherbbjectis to-provide that removal of thestrip and plate may be efiect'edon'removal of thespring, said strip and plate being unattached to the bearing or support members.

The invention and its subsidiary features 'will be fully understood from 'the'following more detailed description by way of exampleof one embodiment thereof, reference being made to the accompanying drawings 'in' which:

Figure l is asectionalside view of a'co mplete switch;

Figure 2 is a top plan view of the body of the switch with cover plate, control knob and cam plateremoved;

Figure 3 is an inverted plan view of the cover plate and cam plate with the relative position of a contact spring 'shown in broken lines;

.Figure 4 is aninverted-plan of the body of the switch;

Figure 5 is a fragmentary detail view; I

Figure 6 is a fragmentary-sectional view taken on'the line 6 6 of Figure 1, and

Figure 7 is a'diagramshowing-a developmentof an operative siirface of -the cam plate-seen in Figure 3.

As shown in thedrawing, the "tiiain 'moving-contac'tl of the switch {Figure -1) is-carried"by"a bifurcated switch plate 2 (Figures 1 and 2), the two legs of which are fulcrumed at their ends on two aligned bearing members or hooks 3 carried by a plate 4 fixed to a casing 5 that forms the switch base. The members 3 are bent to form V-grooved bearing members or hooks which project through slots 300 provided for them in the two legs of the switch plate as shown in Figure 5.

Mounted on the plate 4 between the bearing members 2,798,131 Patented July 2, 1957 3"is a bimetallic strip 6 formed at one end with a tongue 7 which is thrust througha slot in the'plate'4 (seeFigure 6) and attached to an adjusting'lever 9 by which the bimetallic strip 6 can be rocked up and down for a pur- 5 pose which will appear hereinafter. The strip 6 has shoulders 8 adjacent the root of the tongue 7 that bear against the face of the plate 4, which thus constitutes a pivotal bearing support for the strip '6. The bimetallic strip 6 extends between and approximately parallel to the legs of the bifurcated switch plate-2 and has a rockable free end tin-spaced a short distance from the crutch 10 which constitutes a movable free end of the switch plate. In the 'gap thus formedis lodged a'C- spring 11 bent at its ends to form V-grooved pivot bearings one of which rests-against a knife-edge formed 'by the free end6a of the bimetallic strip 6 whilst the other rests'against'a parallel knife-edge "formed by the crutch 10 of the switch plate 2. The construction is such that the 'C-spring 11 constantly applies longitudinal forces of compression and tension to the switch plate 2 and bimetallic 'strip 6 respectively 'and thereby holds these members firmly in engagement with the pivot bearing members 3 and 4 that support them.

The rocking movement of the switch plateis limited in one direction by the engagement of the moving contact '1 with a cooperating fixed contact Hand in theopposite 9, the knob 15 and cam plate 14 being carried by a cover plateattached tothe casing 5. A coiled compression spring 17 acting on the-end of the lever 9'attached to the tongue 7 constantly tendsto rock the bimetallic strip 6 and 'a dj ustinglever 9 in the clockwise direction as seen in'Figure l-so as to 'hold'the cam-follower '16 up to the cam 14.

An electric heating coil '18 wound on a strip of mica orot her suitable material attached to the bimetallic strip 6 is provided for heating the bimetallic strip when current is switched why the closing of the contacts land 12, the 'strip being arranged so that it curls upwards (Figure 1) when heated. The mechanism is adjusted so'that, when the bimetallic's trip'is cold, it assumes a position on the side of the switch plate remote from'the fixed contact; and consequently the pressure of the C-spr'ingnorinally tends to hold the switch contacts closed in th'emanner shown in Figure l. The flow of heating current causes the bimetal "to'curl'upwards so'that it ultimately reaches a position above the switch plate 2. During this movement, as soon as the c-sp'ring 11 haspassed through thedead-centre position, it expands suddenly and causes the switch plate 2 tomove over to the open-contact position with a snap-action. The bimetallic strip 6 then cools and moves the C s pring 1 1 back to its original position so as tore-close the switch contacts, the switch plate Zlag ain moving with a snap action as soon as the C-spring 11 passes the dead centre. Theswitch continues to cyclein this way solong'as the current supply'is maintained.

The ratio between the intervals during which the switch is open and closed respectively during each cycle depends upon the setting of the bimetallic strip 6 and can be altered by adjusting the cam plate 14. The switch controls the average rate of heat supply to a hot-plate by controlling this ratio in a way which is so well known in the art that it need not be described herein.

The construction according to the invention is simple,

inexpensive and reliable. It can readily be designed to have a wide working range of adjustment and may be arranged so that, after being set upwards (i. e. in the direct to increase the heat supply to a hot-plate) the switch will remain closed for a sufiicient length of time to allow the hot-plate to be heated quickly to a temperature at or near that at which it is to be maintained.

As shown in Figure 3 of the drawing, the cam plate 14 is formed at its lowest point with a depression 19 into which the cam-follower 16 falls when the knob is adjusted to an off position, this providing a position in which the device is definitely switched off. To guard against any risk of undesired closing of the supply circuit should the bimetallic strip be cooled excessively when the switch is in this position, an auxiliary contact spring 20 carrying a contact 21 cooperating with a fixed contact 22 is arranged to be controlled by the cam plate 14. This contact spring has a projection 23 which is arranged to bear against the cylindrical edge of the cam plate 14, and

a recess 24 is provided in the edge of the cam plate in such a position that the projection 23 enters the recess and allows the contact 21 to spring away from the contact 22 when the control knob 15 is turned to the off position above referred to. When the knob is moved away from this 0115 position, the projection 23 rides out of the recess 24 and rests on the cylindrical surface of the cam plate 14, the contact 21 being thus pressed into engagement with the contact 22 in all positions of the control knob except the ofi position. The contacts 21 and 22 are so connected in the circuit to be controlled in series with the contacts 1 and 12 that the current supply to the heater under control cannot be switched on when the controls 21 and 22 are separated.

The cam plate 14 is surfacially cammed to move the lever 9 through a convenient range of adjustment as the knob 15 is rotated. This cam surface is shaped as shown in Figure 7 so that it has a working area 25 extending from a low point 26 at one end of its range of adjustment to a high point 27 at the other end of its range of adjustment, the low point coinciding with the depression 19. As can be seen in Figure 7, the cam surface is shaped at 28 so that there is a fair lead over which the follower 16 can ride in either direction. The cam thus has an endless surface over which the follower 16 can ride in either direction so that the knob can be turned from 011 to the full on position or from full on to off without having to be rotated through its whole range of adjustment.

The part shown at 29 is a stop pin provided for so limiting the swinging movement of the bimetallic strip 6 as to prevent it from falling out when the cover plate 30 is removed from the casing 5.

The device is provided with four contact terminals 31 on the bottom of the casing 5 for connecting the contacts 1, 12, 21 and 22 and the heating coil 18 in the r supply circuit of a heater to be controlled.

I claim:

1. A heat-regulating electric switch including in combination a casing, a bearing member secured to the easing, a switch plate engaging the bearing member and attached thereto by a tongue-and-slot connection, said plate having a movable free end, a pair of co-acting contacts within the casing one of which is movable and carried by the free end of the switch plate, a support member secured to the casing, a bimetallic strip Within the casing engaging the support member and attached thereto by a tongue-and-slot connection and having a rockable free end adjacent the free end of the switch plate, an electric heating coil disposed in a position to heat the bimetallic strip and a compression spring connecting together the respective free ends of the switch plate and bimetallic strip and holding the switch plate and bimetallic strip firmly in pivotal engagement respectively with said bearing member and support member, said switch plate being operable by the bimetallic strip through the medium of said spring, relative movement between the free ends of the switch plate and bimetallic strip compressing the spring through a dead-center position, the said spring holding the switch plate firmly in the contacts closed posi tion at normal room temperature.

2. A heat-regulating electric switch including in combination a casing, a bearing member secured to the-casing, a switch plate engaging the bearing member and attached thereto by a tongue-and-slot connection, said plate having a'movable free end, a pair of co-acting contacts within the casing one of which is movable and carried by the free end of the switch plate, a support member secured to the casing, a bimetallic strip within the casing engaging the support member and attached thereto by a tongue-and-slot connection and having a rockable free end adjacent the free end of the switch plate, an electric heating coil disposed in a position to heat the bimetallic strip, and a C-shaped plate spring compressed between the free ends of the switch plate and bimetallic strip and urging the switch plate and bimetallic strip firmly into pivotal engagement respectively with said bearing member and support member, said switch plate being operable by the bimetallic strip through the medium of said spring, relative movement between the free ends of the switch plate and bimetallic strip compressing the spring through a dead-centre position, the said spring holding the switch plate firmly in the contacts closed position at normal room temperature.

3. A heat-regulating electric switch as claimed in claim 2 wherein the switch plate has a slot and the bearing member comprises a leg having a V-groove, the leg entering said slot, the switch plate being held in pivotal engagement with said groove by said C-spring.

4. A heat-regulating electric switch as claimed in claim 2 wherein the bimetallic strip has a tongue and the support member has a slot to receive the tongue, the tongue being held in pivotal engagement with the slotted support member by said C-spring.

5. A heat-regulating electric switch as claimed in claim 2 wherein the C-spring applies longitudinal forces of ten sion and compression to the switch plate and bimetallic striprespectively and thereby holds these parts firmly in pivotal engagement with the bearing and support members respectively.

References Cited in the file of this patent UNITED STATES PATENTS 2,505,689 Rickmeyer Apr. 25, 1950 2,558,219 Kohl June 26, 1951 2,568,323 Dales Sept 18, 1951 2,598,081 Sway May 27, 1952 2,611,855 Turner Sept. 23, 1952 2,623,137 Vogelsberg Dec. 23, 1952 2,646,479 Ashe July 21, 1953 2,658,975 Zuckerman Nov. 10, 1953 2,726,300 Davis et a1 Dec. 6, 1955 

